anyway after installing it i am noticing a loud deceleration pop at the exhaust which i didnt had with the former exhaust system. so i tightened the tailpipe rear and front clamps as there is no gasket in that área. the only 3 gaskets that come with this exhaust system are the manifold to downpipe gasket and the two pipe to pipe 2.5 inches gasket. I even lowered the mixture to 1.5 turns clockwise to lean the mixture and there is still popping at the exhaust. Any clues? My BTDC timing is set to 16 BTDC and My camshaft is a Schneider 274F.

Just to confirm i had no backfire with the former Steel stock exhaust. What could be causing this?

Might sound like a silly question but the exhaust system you've changed to (in particular muffler/exhaust pipe) - is it smaller than previous system you were running.

I used to have an issue where it was a 2 and 1/2" exhaust that ran into a muffler with a 1 and 1/4 exhaust pipe outlet. Used to cause a similar issue, once I changed it to a 2 1/2 all the way through = no problems.

Might sound like a silly question but the exhaust system you've changed to (in particular muffler/exhaust pipe) - is it smaller than previous system you were running.

I used to have an issue where it was a 2 and 1/2" exhaust that ran into a muffler with a 1 and 1/4 exhaust pipe outlet. Used to cause a similar issue, once I changed it to a 2 1/2 all the way through = no problems.

the former one was smaller. This one has a 2.5 diameter bolted from the manifold to the tail pipe. The MSA exhaust comes with a Xcelerator turbo muffler:

Spark plug 3 and spark plug 4 at 2.75 turns clockwise. I am still lean? My car suffer from a fuel percolation problem and if i richen them more they get carbón fouled at idle.

Those plug pics look pretty lean to me, maybe new needles are required. Winding the seat down will richen the mixture throughout the range but mostly at idle as most needles do not have a linear taper.

Those plug pics look pretty lean to me, maybe new needles are required. Winding the seat down will richen the mixture throughout the range but mostly at idle as most needles do not have a linear taper.

Needles? Both carbs were fully refurbished my ztherapy in 2015 including new needles. I dont think the needles are worn.

I'm not suggesting the needles are worn, I'm suggesting they are not the right needle for your engine.
The needle is like the fuel jets on a Weber type carb. The taper on the needle regulates the amount of fuel that passes through the carby for a given piston/damper position.
I think your needles may be too lean for your engine setup.

The popping is due to camshaft duration and overlap, you now have an exhaust system larger, that has less back pressure, thus allowing unburnt fuel to pas through the slightly open exhaust valves.
With back pressure, the unburnt fuel was more kept in the cylinders.
Little bit richer, on mixtures, back timing to 14 or 12 btdc, then check plug colours and run a range or two different, to decrease the plug fouling.

BTW, we visited your country last year, then a run through the Canal. Also Costa Rica, Nicaragua, great beaches, best barbeques, and amazing wildlife! Just regular tourists!

Okay. I found a broken stud which i will replace this weekend including a new manifold to downpipe gasket. Hope it solves the deceleration backfire (popping when releasing the gas pedal) at the tailpipe. I am also enclosing a picture of the new exhaust. Cant stand the popping and not interested on going back to the Steel rail. How much horsepower could i have gained with this new exhaust? I will try and richen the mixture a Little bit more and lower the btdc from 16 to 14 btdc.

I have not stated anyone is wrong here! I am not an expert nor a mechanical engineer! Just trying to understand the deceleration popping at the tailpipe when going down hill or realeasing the gas pedal at 2nd or 3rd gear. I cannot hear it when the car is in neutral and i let the gas pedal go.

The popping is due to camshaft duration and overlap, you now have an exhaust system larger, that has less back pressure, thus allowing unburnt fuel to pas through the slightly open exhaust valves.
With back pressure, the unburnt fuel was more kept in the cylinders.
Little bit richer, on mixtures, back timing to 14 or 12 btdc, then check plug colours and run a range or two different, to decrease the plug fouling.

BTW, we visited your country last year, then a run through the Canal. Also Costa Rica, Nicaragua, great beaches, best barbeques, and amazing wildlife! Just regular tourists!

Next time you come to Panama i will get you a VIP Tour at the New Locks and let you test my 240z!